Discussion in 'Norton Commando Motorcycles (Classic)' started by worntorn, Dec 26, 2018.
Monoblocs and GPs - hard chromed brass slides in zinc bodies, IIRC
No, that’s wrong.
Monoblocs had zinc alloy slides. Pre-Monobloc Amals had brass slides without plating.
I know nothing about GPs.
I've just been doing a winter strip on mine, and was very shocked when I took a close look at the needles....
I bought my bike just over two years ago. It's never ticked over reliably hence the stripdown. It had new Premiers fitted when I bought it which had been hardly used. I've done around 5000 Km since then. I cannot think what could have caused this quite literally "erosion" of (both) needles. Does anybody have any ideas?
Very strange. Ive seen lots of worn out Amal needle jets but not needles.
The old needles seemed to be indestructible.
Looks like corrosion. From water trapped between the needle and the needle jet? Perhaps from washing the bike and putting it away wet???
I agree with the corrosion theory. But it also looks like chrome plate that’s flaking / lifting.
Amal needles aren’t chrome plated are they?
In the first set of three pics, there appears to be a pattern to the corrosion on the needle--fading upward? If that is indeed the case, the fuel may be the culprit. Perhaps methanol fuel additives harboring water molecules in the fuel?
The “erosion” for want of a better word is only on one side of the needles. No sign of any water or any other damage elsewhere in the carbs. I do agree it looks like some sort of acid attack. That needle had a black deposit on it which I just took to be evaporated fuel residue. I felt the roughness so polished that needle with Brasso (Duraglit) wadding so to see it better. Possibly that’s why it looks chrome plated. It’s not. I presume it’s a brass alloy, which I don’t think should suffer from water erosion at this age. I’ll contact Burlen tomorrow and see what they say.
Zinc & brass not compatible with ethanol. At 10% it's going to take some time to show up.
Is it on the area exposed to incoming air flow? If so, do you ride on roads which have been previously salted? What about dust blast through whatever you have as a filter?
any reports of slide bits breaking off?
And, what filters do you run?
I’ve had needles look like they’ve been sandblasted when run without filters...
Standard Ham can filter, I never ride on salted roads, and the slides look like new. I was told that the carbs had only recently been installed when I bought it. I’m not sure which way the blasted side was facing. I’ll have a look at the other one tonight, as I havn’t completely dismantled that one yet. If you zoom in on the real closeup pics it looks almost as though the surface has melted.
I Run standard HamCan with the repro Emgo filter, which is fresh. But why is this relevant to Cliffa's eroded/corroded needles?
I copied your post as to agree with you that Cliffas issue could be related to drawing in detritus.
Sorry for the confusion !
Thanks for all the thoughts. I called Burlen today and the guy I spoke to conferred with colleagues for a few minutes and basically had no more clue that we do. I asked if they had ever had a bad batch of needles, again he conferred and the answer was no. They suggested it was caused by the bike sitting disused. When I got home from work I took the other carb apart, and you can see from the pictures below this one is actually worse, however easier to see a pattern to the damage. The erosion is definitely on the engine side and it starts at 20mm from the tip, and the upper ridge which is visible is 29.9mm from the tip. I would say it extends around the needle 50%. The float bowls and the jets are all clean apart from a light yellow chalky residue from the petrol.
Picture 3 is the filter side of the needle (relatively undamaged).
I'm beginning to think that either that yellow residue is abrasive, or micro rust particles (which is definitely abrasive) are coming from the tank and through the filters (although there has never been any signs of rust in the float bowls).
Engine side you say...
That damage looks like mechanical damage to me, meaning that the needle has been fouling something.
I’d urge you to really carefully check the inside of the needle jets, I’m thinking the vacuum of the engine has been pulling the needle into contact with the needle jet.
But even if I’m right... I really can’t help as to why...
On engine side, eh? Could it be something spewing out from a poor sealing intake valve? Embers of soot residue in a back firing or blow-by sort of situation?
Though quite different in appearance, it reminds of the pitting seen on marine high speed propellers. Apparently this is caused by "cavitation" of the water into microscopic bubbles just after the leading edges of the blades....when the microbubbles collapse at the surface of the blade, they actually do so with enough energy to cause mini fusion events (yes, that's supposedly atomic fusion according to some folks!).
I agree, so using my super cheap super macro clip on smart phone lens (like the others were) I took this..
I didn't like what I saw, but it was not unexpected. On the plus side it gave me the chance to use my genuine AMAL Concentric needle jet holder, (1A, for the use of), which I bought many years ago and never used...